Treat projects in subfolders correctly in `NewFileWizard`

Normally a project is located in the root of the workspace, which would
lead to a physical location like '/workspace/project/file'. But it is
totally valid to have a file in a physical location like
'/worskpace/subfolder/project/file'. In this case the wizard did not
work correctly.

Fixes #1002185
What is `path` relative to? In general, `getFileForLocation` is a bad idea, if you can avoid it. A given file on disk may be mapped to more than one workspace path. Here's the relevant part in the javadoc of this method:

```
 Warning: This method ignores linked resources and their children.  Since
	 * linked resources may overlap other resources, a unique mapping from a
	 * file system location to a single resource is not guaranteed.  To find all 
	 * resources for a given location, including linked resources, use the method
	 * <code>findFilesForLocation</code>.
```